The structural, functional, and conformational aspects of cytochrome c will be elucidated through chemical modification of the surface-localized functional groups, arginine side chains, and thio-ether bridges, reversion of NBS-modified cytochrome c, and investigation of the kinetics of oxidation and reduction with physiological electron acceptors and donors. Detailed kinetic investigations of the physiological function of cytochrome c using chemically modified preparations deemed to reflect preferential derangement of oxidizability or reducibility, and of the reverted form of NBS-modified cytochrome c (form I), will also be conducted to establish whether such preferential derangement does indeed exist, and if so, what the explanation is, i.e. thermodynamic, kinetic, or conformational. Concurrent conformational characterization of the modified preparations and investigation of the oxido-reduction reaction with a conformationally sensitive probe, circular dichroism, and spectroscopic studies will also be performed to establish the interrelationships between the protein conformation and its physiological action. These studies are, in the main, directed toward the identification of the most likely model for the physiological function of the protein and the determination of a mechanism for the transfer of an electron to and from the heme iron of the molecule.